1. Field of the Invention
The present invention relates to an optical crossconect device and a monitoring method of optical crossconnect device and particularly to an optical crossconnect device assuring higher reliability and stability of man optical switch circuit and a monitoring method of an optical crossconnect device.
2. Related Art
With rapid progress of the Internet, capacity of the back-born network is more and more increasing. Recently, an optical crossconnect device has been developed for realizing dynamic path setting and cancellation thereof in unit of the large capacity optical path depending on change of traffics.
This optical crossconnect device can realize the switching operation without conversion of the transmitted optical signal into an electrical signal and therefore can realize reduction in size of the device even when a large capacity traffic is accommodated. However, since the optical crossconnect device accommodates traffics of large capacity, a failure of the optical crossconnect device will give large influence to users utilizing the optical crossconnect device.
Therefore, it is essential to enhance the stability and reliability of the device. For example, the patent document 1 discloses the technology to control the operations of an optical amplifier with a control means comprised within the relevant optical amplifier based on the receiving intensity of the reference optical signal.
However, the invention described in the patent document 1 has a problem that the function does not become effective if the reference optical signal is not received. Therefore, as disclosed in the patent document 2, the technology is known to transmit an optical signal for monitoring to the transmission link even when the optical signal of the particular wavelength of the optical transmission line is not transmitted.
The optical crossconnect device described in the patent document 2 is illustrated in FIG. 1. The optical crossconnect device 10 of FIG. 1 is provided with an optical transmission signal input portion 12, an optical switch circuit 11, an optical transmission signal output portion 13, an optical signal inserting means 15 and an optical signal monitoring means 14. An optical signal for monitoring is transmitted by the optical signal inserting means 15 to the optical transmission line of a switching destination or to a switch-back destination and the optical signal for monitoring is monitored in the optical signal monitoring means 14 within the optical crossconnect device installed at one end of the optical transmission line.
Accordingly, when the transmission line is switched because a failure occurs in the optical crossconnect device or when the transmission line is switched back because the failure is recovered, normal condition and recovery of the optical transmission line where the optical transmission signal of the switching destination or the switch-back destination does not flow and the path in the optical crossconnect device can be monitored and verified.
The Patent Document 1 is a Japanese Published Unexamined Patent Application 2000-312046.
The Patent Document 2 is a Japanese Published Unexamined Patent Application 11-27298.
However, the invention described in the patent document 2 can verify the normal condition of the optical transmission line and the path in the output side of the optical crossconnect device but cannot verify the normal condition of the optical switch circuit forming the optical crossconnect device. Moreover, the switching condition cannot be optimized by this patent document.
Therefore, it is thought, to optimize the switching condition of the optical switch circuit as the core of the optical crossconnect device, that the switching condition of the optical switch circuit is optimized by comparing optical intensity of an input optical signal and an output signal of the optical switch circuit forming the optical crossconnect device in view of improving stability and reliability of the switching condition.
Even in this case, however, an optical signal must always be inputted to the optical switch circuit in order to optimize the internal switching condition by comparing an optical intensity of the input optical signal of the optical switch circuit with that of the output optical signal. However, when the optical signal inputted from the external side disappears, the optimizing operation is stopped. As a result, here rises a problem that verification of normal operation of the optical switch becomes difficult and the stable output cannot be assured when the optical signal is inputted again.
Moreover, when the normal operation is verified by comparing optical intensity of the input optical signal and output optical signal of the optical switch circuit, it is difficult, unlike the signal of electrical level, to verify normal condition only by setting the path in the device. Therefore, it cannot be verify before start of the operation by user that optical switch circuit in relation to the relevant user is surely functioned and therefore failure of the device can be determined after the optical signal of user is actually inputted. For this reason, the failure can be detected initially in some cases after the user signal starts the operation, resulting in the problem that reliability is rather low.